The invention pertains to a drilling column with an air duct for the addition of compressed air to a sledgehammer drilling head, which drilling head has a percussion drilling crown on its lower end and a central connector with a compressed air feed opening on its upper end.
During use of sledgehammer drilling heads, the sledgehammer driven by compressed air is located at the deepest point in the drill hole. The compressed air required for the hammering process is fed through the drilling column consisting of a simple drilling pipe. The compressed air exits from the percussion drilling crown and flows towards the gound surface in the space between the drilled cavity wall and the drill column, whereby the drilled material is forced to the surface.
In order to reach and maintain the required flow velocity for the maintenance of the conveying effect, very high compressed air volumes must be fed. For example, in a drilling diameter of approximately 380 mm and a drill pipe diameter of approximately 150 mm, approximately 25-30 m.sup.3 of compressed air must be applied; the required flow velocity of approximately 30 m/sec in the annulus between the drill pipe and the drilled column wall is thereby accomplished. To achieve this, compressors must work very hard, and they experience a very high energy usage of for example 100 liters of diesel fuel per hour. The operation of diesel motors to drive the compressors represent an elevated environmental load.
The task of the invention is thus to institute a drilling column with a sledgehammer drill head of the type named above such that a significant reduction of the energy usage is accomplished while using conventional sledgehammer drill heads.